Process for determining the combustible content in a gas mixture



J. A, STEIN 1,940,513

G THE COMBUSTIBLE CONTENT IN A GAS MIXTURE Dec. 19, 1933.

PROCESS FOR DETERMININ Filed March 19. 1932 INVENTOR .a 5M

AORVN EY srTeEs PROCESS FOR DETERMINING THE COM- BUSTIBLE CONTENT KN A GAS MIIXTURE Joseph A. Stein, Pittsburgh, Pa, assignor to Eacharach Industrial Instrument Company, a

corporation of Pennsylvania Application March 19, 1932. Serial No 600,044

' 1 Claim. (Cl. 23-232) The invention relates to a process for measing wire occurs under any condition of use. The uring the combustible content of a gas. Ordinarange of use of the apparatus is thus greatly rily the gas to be tested is a gas of combustion broadened and the cost of operation due to rein order to determine the completenessoi complacements reduced to aminimum.

bustion in the apparatus in which the gas is con- Briefly stated, this result is secured by di- '60 sumed,butthe invention is applicabletothe measluting the gas'measured with a volume of air urement or" gases other than gases of combustion. which bears a definite relation 'to the volume The apparatus employed in the practice of the or" gas used, and which will guard the apparatus process is of the general type shown in the patent against failure of the catalyzing wire regardless to Max Moeller No. 1,562,243, wherein the temof changes in the composition of the; gas whose perature of a catalyzing wire as aiiected by the percentage of combustible is under determinagas burned adjacent the wire is used as the detion. One form of apparatus suitable for cartermining factor in ascertaining the percentage rying out the process is shown in the accompaof combustible (gas) in the gas tested. Appanying drawing, wherein:

l5 ratus of this type has been used with some suc- The figure is a diagrammatic view partially in cess in measuring the CO, H2 and other comsection. v bustibles in which the amount of combustible is The construction involves the use of a Wheatlow, that is not over 4 to 8 per cent of the gas stone bridge arrangement in which 1 and 2 are tested, but serious difiiculties have attended the standard resistances and 3 and 4 are a pair of 20 use of the apparatus when the combustible conresistance wires located in the chambers or tubes tent exceeds these percentages, which it is the 5 and 6. The resistance wires are preferably purpose of the present invention to overcome. made of platinum alloy although any other suit- One of the main diificulties is the fact that the able alloy may be used which will act as a catapparatus has been unreliable, due to the temalyzing agent when exposed to contact with gases 5 porary or permanent failure of the catalyzing of combustion and oxygen. The gases to be wire to function under varying conditions. A measured are caused topass through the chamcondition referred to as. poisoning or contami ber 5'while the chamber 6 contains atmospheric nation or" the catalyzing wire arises when the air, the two wires which are ofthe same macombustible in the gas increases above a certain terial, length and cross section thus serving as 30 point. At such time thecatalysis may fall so a basis of comparison as is well known in the that the device ceases to record or indicate at art. all. In other cases, the device continues to in- The points 7 and 8 are connected by the wires. dicate the percentage of combustible, but does 9 and 10 forming a circuit in which is located an so incorrectly. This failure is ordinarily merely indicating instrument, such as the galvanometer 5 temporary and is remedied when the combustible 11. Operating current is supplied from a bat- 9i) content decreases below a certain point, but in tery 12 in the circuit 13, 14-. and this circuit is some cases it becomes permanent and a new provided with a small variable resistance 15 and catalyzing wire has to be substituted. The reliathe ammeter 15a for the purpose of adjustment. bility of the device is also impaired when the The gas of combustion to be analyzed is con- 40 catalyzing wire is overheated dueto catalytic. ducted to and from the tubular chamber 5 by "96' combustion of high percentages of combustible I the pipes 16 and 17, of which 16 is the inlet and. gas which is entirely apart from the failure of 17 the outlet, the inlet pipe being provided with the wire due to poisoning. These liabilities to the orifice member 18. Connected to the gas infailure have greatly retarded the introduction let pipe 16 is an air inlet pipe 19 whose outer 5 and use of the apparatus, which inother respects, end is provided with a cavity having a cotton both as to cost and ease of use, is admirably filter 20 therein. Admission of air to the cavity adapted for testing gases. is afforded by the opening 21, and the orifice My invention overcomes the diificulty above member 22 regulates the flow to the pipe 16. The outlined, making the apparatus entirely reliable filter 20 protects the pipe and its orifice from under any condition of use, so that no poisoning clogging with dirt.

or" the wire will occur or overheating thereof. The The current supplied to the wires 3 and 4 is process may be employed for accurately detersuch as to heat them .to a point Where the wire 3 mining the combustible, when such combustible will ignite the combustible in the stream of gas ranges from 0 to 100 per cent of the gas tested, by catalysis. The resulting combustion raises the v 55 and no poisoning or overheating or" the catalyztemperature of the wire 3 still further, whereby the resistance of the latter is increased by an amount proportional to the heating eflect of the combustible contained in the gas being tested. The change in resistance of the wire unbalances the circuit of the Wheatstone bridge, of which the heated wire 3 is one of the branches, and this causes a current which varies as the heating effect of the combustible in the gas to fiow through the galvanometer 11 which is calibrated to read directly in per cent of CO and/or H2, or any other combustible which it is desired to measure.

Heretofore in the operation of apparatus of this character, it has been the practice to admit an amount of air through the pipe 19 which is in excess of that required to support combustion, the ratio of the volume of air to gas being in all cases 1 m1 or less, and such proportion has given a satisfactory operation when the percentage of combustible in the gas was relatively low,

.but when attempts have been made to use the apparatus in testing gas having a high combustible content, the apparatus has been unsatisfactory due to the poisoning or overheating of the catalyzing Wire, as heretofore explained.

I have discovered that the range of the apparatus may be increased to any desired extent, without shortening its life, by a proper dilution with air of the gas tested, preliminary to its admission to the chamber carrying the catalyzing wire.

With a proper dilution, the instrument may be used to indicate accurately the amount of combustible in the gas running up to 100 per cent, so that the one apparatus may be used for all classes of work. I have found that the volume of diluting air in order to insure a reliable and continuous operation of the apparatus under the widely varying conditions of combustible content must be very great, preferably in the neighborhood of twelve volumes of air to one of gas. Stated differently, the volume of air should be such that with a maximum combustible content in the gas tested, the air should carry an oxygen content which is at least twice that required to complete the combustion of the combustible content. In its preferred form, therefore, the process contemplates the admixture of a quantity of air with the gas which is many times in excess of that heretofore employed and far beyond that required to support combustion even when the combustible content may approach 100 per cent of the gas tested. The utility of the apparatus and process is not limited, however, to use of the particular ratio of air to gas specified, as lower range apparatus, in which the percentage of combustible in the gas tested is always low, will operate satisfactorily with smaller volumes of diluting air. For instance in the testing of gases in which the combustible never ranges over 16 per cent, the volume of air to that of gas may range as low as 2 to 1.

In the particular apparatus shown, the desired proportion of air to gas is secured by making the orifices 18 and 22 of the requisite relative size, the air orifice 22 being about 12 times the cross sectional area of the orifice 18. The volume of diluting air thus provided not only prevents any poisoning of the wire 3, but also prevents any overheating thereof. In the particular construction shown, the relative volumes of air and gas are governed by the size of the orifices l8 and 22, but the process is not limited to. this means for controlling the relative volumes of gas and air. The 7 air may be introduced under pressure so that the volume introduced may be controlled in the practice of the process in this manner rather than by-the size of the orifice.

The apparatus will ordinarily be calibrated to electrically, and in supplying said gas through said space, the step of mixing said gas preliminary to its introduction into said chamber with a volume of diluting air which is greatly in excess of the volume of gas and in all cases has an oxygen content at least twice the theoretical amount necessary tosupport the combustion of the maximum combustible content in the gas.

' J. A. STEIN. 

